1. Field of the Invention
The present invention relates to a motor grader. More specifically, the invention relates to a motor grader with a multi-function operation lever which performs more than one function.
2. Description of the Related Art
A typical example of the conventional motor grader is illustrated in FIGS. 1. In the shown construction, the motor grader is provided with a draw bar 2 swingably mounted on the front end of a vehicle body 1. Left and right lifting cylinders 3 and 4 and a transporting cylinder 5 are connected between the draw bar 2 and the vehicle body 1. A swing circle 6 is mounted on the draw bar 2 for swing motion by means of a hydraulic swing motor 7. A blade 9 is mounted on the swing circle 6 via a bracket 8 of the latter for movement in lateral directions by means of a blade shifting cylinder 10. In addition, a leaning cylinder (not shown) is provided for front wheels 11 for leaning in the lateral directions.
Also, there are various known motor graders. For instance, a motor grader having a scarifier movable in the vertical direction by means of a scarifier cylinder has been known. Furthermore, a motor grader is known having an articulated vehicle body for arcuating by means of a steering cylinder.
In order to control the operations of various cylinders, a hydraulic swing motor and so forth, an output pressure of a hydraulic pump as a hydraulic pressure source is distributed to respective cylinders and the hydraulic motor via direction control valves. For controlling operation of respective direction control valves, a plurality of operation levers are provided in a work implement operating device of the motor grader. One example of the work implement operating device is illustrated in FIG. 2. As can be seen from FIG. 2, a plurality of operation levers which are generally represented by the reference numeral 12, are provided at both sides of a steering wheel 13. Respective operation levers 12 are connected to corresponding direction control valves via a link mechanism. In the example shown in FIG. 2, a right blade lifting operation lever 12a, a leaning operation lever 12b, and a blade shifting operation lever 12c are arranged at the right side of the steering wheel 13, and a draw bar shift operation lever 12d, a steering operation lever 12e, a swing circle operation lever 12f, a scarifier operation lever 12g and a left blade lifting operation lever 12h are arranged at the left side of the steering wheel 13.
With the operation device set forth above, since a plurality of operation levers are connected to the corresponding direction control valves by means of link mechanisms, the construction becomes complicated. Furthermore, for operating the work implement, one of more operation levers corresponding to a desired behavior of the work implement have to be selected, thus to make an operator's operation complicated. In addition, a plurality of operation levers arranged at both sides of the steering wheel may degrade forward sight.
For example, when the blade 9 is to be lifted or tilted, the left and right blade lifting operation levers 12a and 12h are operated. Also, when the blade 9 is to be shifted in the lateral direction, the blade shift operation lever 12c is operated, and when the swing circle 6 is to be swung, the swing circle operation lever 12f is operated. In addition, when the work implement has to be operated while the vehicle is running, the operator is required to operate both the steering wheel 13 and the operation levers 12 by frequently moving the hands between the steering wheel 13 and one more of the operation levers 12.
On the other hand, when the blade 9 is to be pivoted to vary an angle formed between the longitudinal axis of the vehicle body 1 and the blade 9, which angle will be hereafter referred to as a propulsion angle, the relevant operation levers 12 are operated to switch the valve positions of the corresponding direction control valves to drive the hydraulic swing motor 7 to pivot the blade 9 together with the swing circle 6. However, during this operation, the left and right ends of the blade 9 move along an arc so that the lateral positions of the left and right ends of the blade 9 may be differentiated between the positions before and after pivoting. Namely, when the propulsion angle of the blade is varied, the position of the ends of the blade 9 should be varied. This may cause a problem to cause collision of the blade with the shoulder of the road due to a difference in positions of the ends of the blade. To avoid this, it becomes necessary to cause a lateral shift of the blade upon varying the propulsion angle. This clearly requires extra operation for the lateral shifting of the blade to make the operator's operation more complicated.
On the other hand, in the prior art, there has been proposed a blade angle control device to automatically control a blade angle irrespective of variation of tilt angle of the vehicle body and/or the propulsion angle of the blade. The blade angle control device includes a target blade angle setting means, such as a dial, switch or so forth. The blade angle control device is designed to control the blade angle to the target angle set through the target blade angle setting means. For varying the target blade angle, it requires the manual operation of the operator against the target blade angle setting means.
Therefore, such blade angle control device is not applicable for the cases where the left and right cant of tilt angle varies sequentially with curving of the working road, or where the target blade angle has to be varied at the intersection with the other working road, for substantial difficulty occurs in setting or varying the target blade angle an appropriate value by the operator.
Also, when the blade is to be lifted up or down, both of the direction control valves corresponding to left and right lift cylinders 3 and 4 are to be operated. This requires operations of the left and right blade lifting operation levers 12h and 12a. Then, both hands of the operator are used for operating the left and right blade lifting operation levers 12h and 12a to make it impossible to operate the steering wheel 13. In addition, during lifting up and down of the blade 9, the blade may cause lateral shifting due to presence of the lateral feeding cylinder 5. Therefore, the operation of the lateral feeding cylinder 5 is further required to make the operator's operation more complicated in the extent that a qualified operator is required for performing the operation set forth above.